For carrying out a reaction process, systems are required in which the individual particles of the reactants may quickly be brought into close contact with one another. This requires thin layers for keeping the transport paths short and for making the surface area of the process space large. This also requires intensive mixing within the layer, removal of unnecessary components from the reaction zone, and rapid heat exchange.
There are a number of processes for carrying out reactions which take place in the liquid phase or at the interface between the liquid and the gas phase.
A process employing a stirrer-equipped vessel is generally used in the present state of the art. The components are introduced into the stirrer-equipped vessel along various points thereof and the individual particles are brought into contact with one another by circulating the mixture by means of rotating stirrers. The heat is introduced and dissipated through the walls of the vessel.
Unfortunately, this process is attended by several disadvantages. These include the long transport paths within the phase, the non-uniform treatment of the product, the wide residence time spectrum, the poor heat and mass exchange, the high investment costs and the operational unreliability attributable to the mechanical stirrers.
Another process employs the bubble column which is particularly suitable for interfacial reactions between gas and liquid. The bubble column consists of a multi-plate column through which the liquid flows. Gas bubbles pass through the liquid on each plate. There is a large interface between liquid and gas where the reaction takes place. The heat is again introduced and dissipated through the walls of the tube. Disadvantages of this process include the fact that it is limited to low viscosity liquid media, to a large liquid volume, by poor heat exchange and by the inevitable back-mixing associated with a wide residence time spectrum.
A process which is particularly suitable for highly viscous products is carried out in a double-flighted or four-flighted screw. Due to the contra-rotation of the screws, the components are continuously mixed in an intensive manner. Heat is introduced through the screw shafts or through the walls and dissipated through the walls. Components which are no longer required may be drawn off through vapor domes. Disadvantages of this process include high costs, the fact that it is limited in its application to highly viscous products, the fact that there are rotating parts and the small phase separation surface. The energy generated by the screw shafts is also a troublesome factor in exothermic processes because it has to be dissipated as heat in addition to the heat generated by the reaction.
Reactions may also be carried out in a tube reactor which consists of straight tube sections separated by bends in which the liquid changes direction and, in doing so, is intensively mixed. The reaction takes place as the liquid flows through the tube. Heat exchange occurs directly with a heat carrier in the jacket space. Disadvantages of carrying out reactions in this way include the fact that the entire cross-section of the tube is filled with the product liquid, which necessitates long transport paths, the fact that mixing is limited to the curved sections and the fact that there is no possibility of mass exchange.
Other known tube reactors consists of several straight tubes joined together by bends. Reactors of this type, which are intended solely for gas-liquid reactions, may only be used with liquids of low viscosity. The danger of gas bubbles being entrained, resulting in different treatment of the individual product particles, is very considerable which reduces, on the one hand, the efficiency of the process and, on the other hand, the quality of the product.
An object of the present invention is to provide a process in which starting components, of which at least one must be a liquid, are brought into contact with one another in a static apparatus so intensively, even with high viscosity levels, that one or more reactions take place at high velocity. All the secondary gases and vapors which accumulate during the process and which are no longer required should be directly removed from the reaction zone and the optimum reaction heat should be able to be adjustable by heat exchange over the shortest possible distance.